Quad and Tri shield coax

[Ralph]

Can anyone tell me the difference between Quad and Tri shield coax?
I know that it has an extra layer of shielding, but as all the shields touch
I can't see what difference it makes.

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[robert casey]

Ralph wrote:

Can anyone tell me the difference between Quad and Tri shield coax?
I know that it has an extra layer of shielding, but as all the shields touch
I can't see what difference it makes.

--
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More layers of shielding will make for less leakage from

or to the center conductor.

 

[Ralph]

I understand that, but if they are all touching wouldn't they act as one
layer?

"robert casey" <wa2ise@ix.netcom.com> wrote in message
news:kxaVd.12020$Ba3.163@newsread2.news.atl.earthlink.net...

Ralph wrote:

Can anyone tell me the difference between Quad and Tri shield coax?
I know that it has an extra layer of shielding, but as all the shields
touch
I can't see what difference it makes.

--
remove n u m b e r s to reply


More layers of shielding will make for less leakage from
or to the center conductor.

 

[Fred Ferd]

"Ralph" <r2a3l4p6h_s7m8i9t0h@bigpond.com.nz> wrote in message
news:yuCVd.182447$K7.132575@news-server.bigpond.net.au...

I understand that, but if they are all touching wouldn't they act as one
layer?

Wouldnt 5000 meters of layer of lead act as if it just a film 0.1mm thick ??

NO, the thickness sets the impenetratability for EM.

Yeah I thought the benefit of extra shielding would be improved by having
the layers insulated from each other, but thats not so. maybe because it
increases capacitance to do that.

 

[Terry Given]

Ralph wrote:

I understand that, but if they are all touching wouldn't they act as one
layer?

yes, but a thicker layer. *IF* they are in good electrical contact.
Often they are not, and the contact resistance is a lot higher than the
longtitudinal resistance of the shield.

A good reference is:
Cable Shielding for EMC, A. Tsaliovich, Chapman Hall, ISBN 0-442-01425-2

the maths is a little bit crunchy, but can safely be ignored - his
waffly stories are excellent, and the graphs of shield transfer
impedance (for a variety of shield combinations) carry a wealth of
useful data.

"robert casey" <wa2ise@ix.netcom.com> wrote in message
news:kxaVd.12020$Ba3.163@newsread2.news.atl.earthlink.net...

Ralph wrote:


Can anyone tell me the difference between Quad and Tri shield coax?
I know that it has an extra layer of shielding, but as all the shields

touch

I can't see what difference it makes.

--
remove n u m b e r s to reply



More layers of shielding will make for less leakage from
or to the center conductor.

maybe. depends on the execution of each shield, eg weave coverage, braid
angles, foil pitch & overlap etc, blah blah blah. Many ratshit shielded
cables exist, and many multiple-shield cables are not worth the money.

Cheers
Terry